1. Field of the Invention
This invention relates to an internal combustion engine knock controlling apparatus for controlling a knock phenomenon that occurs in an internal combustion engine.
2. Description of the Related Art
Conventionally, a method of detecting a knock phenomenon that occurs in an internal combustion engine by a sensor fitted directly to a block of the internal combustion engine, i.e., a vibration sensor (hereinafter referred to as a “knock sensor”) has been known, as disclosed in, for example, JP-A-2006-22648 (Patent Document 1). It is known that when knock occurs during the operation of the internal combustion engine, vibration in a specific frequency band occurs according to the bore diameter of the internal combustion engine or the vibration mode of knock. By measuring the vibration intensity in the specific frequency (hereinafter referred to as a “knock signal”), knock detection is performed.
A knock controlling apparatus that suppresses knock by correcting ignition timing toward the retard side when knock is detected and minimizes torque reduction by reverting ignition timing to an advance side when knock is not detected is also known, as disclosed in, for example, JP-A-56-115861 (Patent Document 2). It is known that an internal combustion engine has the following characteristic. When ignition timing is advanced, the output torque of the internal combustion engine improves but knock occurs more easily. On the other hand, when ignition timing is retarded, the output torque of the internal combustion engine decreases but knock does not easily occur. The above-mentioned knock controlling apparatus is such that, when knock is detected, ignition timing is corrected to the retard side, while when knock is not detected, ignition timing is reverted to the advance side, whereby the internal combustion engine is controlled to operate at the knock limit ignition timing at which the maximum torque is generated while the occurrence of knock is suppressed. However, when, for example, the internal combustion engine is operated with a low load, there are cases in which knock does not occur even if the ignition timing is advanced to the timing at which the torque becomes maximum. In such an operation region, the above-described knock controlling is unnecessary.
In these kinds of knock controlling apparatuses, the knock determination threshold value for determining knock is generally set based on standard statistics such as the mean value and the standard deviation of the knock signal calculated by filtering a knock signal. For example, various methods of setting the knock determination threshold value are known, as disclosed in JP-A-4-140454 (Patent Document 3). In one method, the threshold value is set using the mean value of knock signals calculated by filtering the knock signal, and the gain and offset that have been matched in advance. In another method, the threshold value is set using the mean value of the knock signal and the standard deviation of knock signal calculated by filtering the mean value of knock signal and the deviation of knock signal.
In these methods, when the internal combustion engine is in a steady operating state, in which the revolution speed of the internal combustion engine and the output of the internal combustion engine is almost constant, variations in the mean value and standard deviation of the knock signal are lowered to suppress variations in knock determination threshold value, by setting the filter coefficient of the filtering process to be large, that is, by setting the cut-off frequency to be low. Thereby, a stable operating condition in which torque fluctuation is small can be obtained.
In addition, when the internal combustion engine is in a transitional operation state, in which the revolution speed of the internal combustion engine or the output of the internal combustion engine is increasing or decreasing, the response characteristics of the standard statistics of the knock signal such as the mean value and standard deviation of the knock signal is raised to control the knock determination threshold value to have good tracking capability by setting the filter coefficient of the filtering process to be small, that is, by setting a high cut-off frequency. Thereby, erroneous detection of knock can be suppressed.
U.S. patent application Ser. No. 13/290437, filed by the present applicant et al., has proposed a method of switching over the filter coefficients used in the filtering process for calculating the mean value and standard deviation of the knock signals between in a steady operating state and in a transitional operation state. The purposes thereof are to detect the transitional operation state without delay and to match the transition correction amount, including the degree of accelerating/decelerating, the transition correction duration, and the transition correction amount decrease speed, with a smaller number of steps. A filtering process is carried out for each of plural operating state values, and a transition correction factor is calculated based on a value obtained by normalizing a deviation between the operating state value and the filtered operating state value by a representative value. The filter coefficient used for the filtering process for calculating the mean value and the standard deviation of knock signal is corrected using the obtained transition correction factor, so that the knock determination threshold value in the transitional operation state can be appropriately set to suppress erroneous detection of knock.
[Patent Document 1] JP-A-2006-22648
[Patent Document 2] JP-A-56-115861
[Patent Document 3] JP-A-4-140454
However, the method proposed in U.S. patent application Ser. No. 13/290437 uses a predetermined value that has been matched in advance, as the filter coefficient used for the filtering process corresponding to the operating state value. Consequently, since the filter coefficient used in the filtering process for calculating the mean value and standard deviation of the knock signal is corrected by the transition correction factor, the response characteristics of the mean value and standard deviation of the knock signal are improved. On the other hand, a problem is that the transition correction factor is kept calculated after tracking of the mean value and the standard deviation of the knock signal has been completed, that is, the correction period of the filter coefficient used for the filtering process for calculating the mean value and standard deviation of the knock signal is inappropriate, so knock detection cannot be performed appropriately.
Another problem is as follows. When the calculation process period for the transition correction factor is different from the calculation process period for the mean value and standard deviation of the knock signal, the response characteristics of the filtering process for calculating the transition correction factor and the response characteristics of the filtering process for calculating the mean value and standard deviation of the knock signal become different from each other. Consequently, the correction period becomes inappropriate, and knock detection cannot be performed appropriately.
The just-mentioned problem will be explained with reference to FIG. 6. FIG. 6A shows the first operating state value and the filtered value thereof in a transitional operation state. FIG. 6B shows the first post-normalization operating state value deviation calculated based on the first operating state value. FIG. 6C shows the second operating state value and the filter value thereof. FIG. 6D shows the second post-normalization operating state value deviation calculated based on the second operating state value. FIG. 6E shows the transition correction factor calculated by summing the first post-normalization operating state value deviation and the second post-normalization operating state value deviation. FIG. 6F shows an operation example of the knock signal in a transitional operation state, the mean value of the knock signal in a state in which its response characteristics are raised by a transition correction factor, and the knock determination threshold value that is set according to the mean value of the knock signal, and as seen at point A in FIG. 6F, it shows the state in which knock has occurred immediately after the transitional operation state.
According to the method proposed in U.S. patent application Ser. No. 13/290437, the filter coefficients used in the filtering process for calculating the operating state values are predetermined values. Therefore, even after tracking of the mean value of the knock signal has been completed by raising the response characteristics by a transition correction factor, the transition correction factor is kept calculated. Consequently, the response characteristics of the mean value of the knock signal remains quick, so the knock determination threshold value is not stabilized. Therefore, knock detection cannot be performed appropriately, or knock detection failure occurs.